I had a Sig P226 .40 slide milled by Vulcan Machine back in July and they did a beautiful job. The spring is exposed and compressed by the optic, but they mill the front recoil lugs into the slide. They are not perfectly round, but they will obviously take a load off of the mounting screws. I have had 100% function and reliability so far. Vulcan machine also gave me fast turn around and they have excellent communication. I am getting ready to send them another P226 9mm and P229 9mm slide for milling, so I am obviously willing to recommend them.

I think you would be happy with their work and their customer service!